This invention relates to a gas-liquid contacting apparatus.
Perforated trays with downcomers are the most commonly used internals in industrial columns for contacting a gas and a liquid. In such columns, liquid flows across the trays and down through the downcomers, from tray to tray, while gas permeates upwardly through the trays foaming liquid thereon.
U.S. Pat. No. 3,410,540, dated Nov. 12, 1968, Bruckert, describes perforated trays having multiple downcomers. With these trays, multiple downcomers, e.g. five downcomers, extent along parallel paths across the tray, more or less equally spaced across the column. The multiple downcomers of adjacent trays extend along paths which are at right angles to one another so that outlets from the downcomers can be arranged to direct liquid onto the tray below, between its downcomers, as will be seen from xe2x80x9cPerformance of Multiple Downcomer Traysxe2x80x9d W. V. Delivicki and J. L. Wagner, Chemical Engineering Progress, Vol. 66, No. 3, March 1970, pages 50-55, and xe2x80x9cMD Trays Can Provide Savings in Propylene Purificationxe2x80x9d R. D. Kirkpatrick, Petrochemicals, The Oil and Gas Journal, Apr. 3, 1978.
In summary, multiple downcomer trays have liquid seals formed above spouts at lower ends and so avoid using any tray area for the this purpose, thus increasing the tray active area, use shorter liquid flow paths across the trays, thus reducing hydraulic gradients on the trays, spread the liquid loadings over the greater number of downcomers, thus allowing better control of foam height over wider ranges of liquid and gas flow rates providing higher rangeability, and allow the downcomers to be used as a primary support for the tray.
While these multiple downcomer trays are an advance in the art, a problem exists with them in that the downcomers give poor liquid flow distribution on the tray below which results in stagnant areas thereon with regard to liquid flow thereacross. U.S. Pat. No. 5,382,390, dated Jan. 17, 1995, M. R. Resetarits and M. J. Lockett, teaches minimizing this problem by providing gas directing slots in the tray for directing gas towards the closet downcomers and reduce froth height.
While the gas directing slots reduce the stagnant liquid flow area to some degree, there is still a need for a gas-liquid contacting apparatus wherein the formation of stagnant liquid areas on the trays is substantially reduced.
According to the present invention there is provided a gas-liquid contacting apparatus, comprising
a) an upwardly extending casing having a liquid inlet to, and a gas outlet from, a top end portion thereof, and a gas inlet to, and liquid outlet from, a lower end portion, thereof,
b) a plurality of perforated tray assemblies partitioning the casing at different levels between the said upper and lower portions thereof, each tray assembly comprising an array of perforated sheets, at least major portions of which are separated from one another by a lattice-like-pattern of liquid receiving channels, and for each pattern of channels,
c) a correspondingly patterned downcomer weir and duct means encasing those channels and receiving liquid from the perforated sheets separated thereby,
d) liquid delivery means attached to duct portions, of the weir and duct means, for maintaining a liquid seal in the duct portions, and for delivering liquid from the duct portions to a central region of each perforated sheet immediately therebelow
Portions of the weir and duct means of each upper tray assembly may cross the said central regions of the said perforated sheets immediately therebelow.
The duct portions of a weir and duct means are preferably interconnected to more evenly distributed the flow of liquid over the tray assembly immediately therebelow.
The lattice pattern may be square shaped.
The duct portions of adjacent tray assemblies may extend across the casing in substantially the same directions, with the duct portions of adjacent tray assemblies laterally displaced from one another.
The duct portions may follow a lattice pattern formed of an odd number X of parallel ducts extending in one-direction, crossed by an even number Xxe2x88x921 of parallel ducts extending along a direction at right angles thereto, and the ducts may be spaced sideways from one another, with the odd number ducts of adjacent tray assemblies extending at right angles to one another, so that the ducts of the upper tray assemblies pass over central regions of the perforated sheets of the tray assembly immediately therebelow.
The ducts may be troughs, and the liquid delivery means may be grills at the bottoms of the troughs.
The upwardly extending casing may be circular in plan view, and the liquid delivery means may further comprise closed topped casings attached to both sides of portions of a duct which extend over segment shaped portions of the perforated tray assembly therebelow, the interior of each closed topped casing may be open to the interior of the duct, to receive liquid therefrom, and may have an open bottom for discharging that liquid, and a grill may be provided over each open bottom, each grill may have slots which extend transversely to the longitudinal direction of the duct to which it is attached.
Preferably, the distances between adjacent ducts are of equal magnitude.
Liquid passages may be provided in the form of a series of openings in the weir portions.
The ends of weir portions of the Xxe2x88x921 ducts may be spaced from the weir portions of the X ducts to provide liquid paths around the Xxe2x88x921 parallel ducts.
Perforated side walled catchment trays may be provided beneath the grills.
Liquid flow distributing baffles may be provided on weir portions of the weir and duct means.
End portions of the outer ones of the three ducts may be angled in plan view to closely follow the curvature of the casing, when the casing is circular.
In this specification, lattice-like-patterns includes lattice-like patterns where,
i) liquid receiving channels are interconnected at lattice intersection, and
ii) liquid receiving channels terminate before lattice intersection.